Hot water apparatus

ABSTRACT

A hot water apparatus is provided in which heat recovery is performed as much as possible allowing drain to be generated and excellent heat efficiency is achieved without providing a plurality of heat exchangers by effectively evaporating generated drain. In a water heater  1 , the drain evaporator  11  is disposed inclining so that its side facing the high temperature portion of the heat exchanger  10  is at a lower position. The generated drain drops on the drain receiver guiding portion  28 , and moves by its own weight to the side facing the high temperature portion. Then the drain is heated and evaporated. In this evaporation, the same amount of heat as that of recovered latent heat is discharged to the exhaust gas, however, sensible heat can be recovered as much as possible without limiting drain generation in the heat exchanger  10.

BACKGROUND OF THE INVENTION

This application claims the benefit of Japanese Patent ApplicationNumber 2003-421824 filed Dec. 19, 2003, the entirety of which isincorporated by reference.

1. Field of the Invention

The present invention relates to a hot water apparatus, for example awater heater, which includes a heat exchanger for heating flowing waterby combustion heat of a burner.

It should be noted that in the following explanation “exhaust gas” meansnot only exhaust gas passing through a heat exchanger but also hotexhaust gas generated by burner combustion before heat exchange.

2. Description of Related Art

Generally, as an example of a hot water apparatus, a water heater has aheat exchanger with which a cold water supply pipe and a hot wateroutlet are connected, and a burner which heats the heat exchanger. Withthis configuration, the heat exchanger heats flowing water by combustionexhaust heat from the burner, and hot water is discharged from the hotwater outlet.

In this water heater, a heat exchanger of the fin tube type is usuallyused in which temperature of exhaust gas passing between fins is noteven. That is, the temperature of the heat exchanger becomes colder withbeing close to its water entrance side, resulting that drain is oftengenerated at the water entrance side. In order to prevent draingeneration, heat exchange is limited under the condition thattemperature of exhaust gas passing through gaps between the fins at thewater entrance side is kept above the dew point (approximately 50-60°C.). According to the above, at the water exit side of the heatexchanger hot exhaust gas is discharged wastefully even if more heatexchange could be performed without generating drain.

In order to solve the above problem, a condensing water heater is known,in which another heat exchanger is provided at the downstream of theexhaust route for improving thermal efficiency. In a condensing waterheater recited in Japanese Patent Publication of unexamined applicationNo. 2002-195645, a main heat exchanger is provided at the upstream ofthe exhaust gas route and a secondary heat exchanger is provided at thedownstream thereof. In the main heat exchanger sensible heat isrecovered under limited heat exchange for the purpose of preventingdrain generation, and in the secondary heat exchanger provided at thedownstream of the main heat exchanger sensible heat and latent heat arerecovered until drain is generated.

In the above-mentioned heat exchange, drain generated in the secondaryheat exchanger becomes acidic, reacting chemically with SOx or NOx inthe exhaust gas. Due to this, neutralization process is required beforethe drain is discharged into a common drainage route, such as sewage.Then, a drain neutralization apparatus is required, and thus the cost isfairly expensive. Moreover, it is necessary to change a neutralizingagent used in the neutralization apparatus periodically, whichdeteriorates utility of the condensing water heater.

In order to solve the above problem, a water heater is proposed in whichdrain generated in the secondary heat exchanger is evaporated by beingcontacted with the exhaust gas as disclosed in Japanese PatentPublication of unexamined application No. 2002-98413.

The above-mentioned water heater has a main heat exchanger, a secondaryheat exchanger and a drain evaporator in a common exhaust gas route.Firstly, sensible heat in the exhaust gas is recovered in the main heatexchanger. Thereafter, drain is generated, and latent heat and sensibleheat which has not been recovered in the main heat exchanger arerecovered in the secondary heat exchanger. Lastly, drain generated inthe secondary heat exchanger is evaporated by heat of exhaust gas in thedrain evaporator.

According to this water heater, the same amount of heat as that oflatent heat recovered by the secondary heat exchanger is used for drainevaporation, resulting that latent heat is not recovered. However,recovery efficiency regarding sensible heat is improved compared to anordinary water heater.

However, in both above-mentioned prior arts, the main heat exchanger andthe secondary heat exchanger are provided at two stages, that is, at theupstream and the downstream on the exhaust gas route, which makes thestructure of the heat exchanger enlarged and complicated. Therefore, itcosts expensive and the needs for downsizing is not satisfied.

Moreover, a large quantity of sensible heat to be recovered remains inthe main heat exchanger because heat exchange is limited for the purposeof generating no drain, so that heat exchange is performedinsufficiently in the secondary heat exchanger even if recovering theremained sensible heat is attempted.

In order to solve this problem, an object of the present invention is toprovide a hot water apparatus which recovers heat as much as possibleallowing drain to be generated and achieves excellent heat efficiency byeffectively evaporating generated drain without providing a plurality ofheat exchangers.

SUMMARY OF THE INVENTION

In order to solve the above problems, in accordance with a first aspectof the present invention, a hot water apparatus includes a burner forburning fuel gas in a combustion chamber, and a heat exchanger forheating flowing water in a heat transfer tube by combustion heat of theburner, wherein drain generated at a low temperature portion of the heatexchanger is evaporated by hot exhaust gas passing through a hightemperature portion of the heat exchanger.

A hot water apparatus in accordance with a second aspect of the presentinvention, there is provided a hot water apparatus according to thefirst aspect, wherein a guide means for guiding the generated drain intoa flowing route of hot exhaust gas passing through the high temperatureportion of the heat exchanger is provided.

A hot water apparatus in accordance with a third aspect of the presentinvention, there is provided a hot water apparatus according to thesecond aspect, wherein the guide means has a drain receiving andevaporating unit provided at the downstream of the exhaust gas route ofthe heat exchanger for receiving drain, and said drain receiving andevaporating unit guides drain from the side facing the low temperatureportion of the heat exchanger to the side facing the high temperatureportion thereof.

A hot water apparatus in accordance with a fourth aspect of the presentinvention, there is provided a hot water apparatus according to thesecond aspect, wherein the guide means has a drain receiving andevaporating unit provided at the downstream of the exhaust gas route ofthe heat exchanger for receiving drain, and the drain receiving andevaporating unit is disposed inclining so that its side facing the hightemperature portion of the heat exchanger is at the lowest position.

In the hot water apparatus according to the first aspect having theabove-mentioned configuration, water passing through a transfer tube ofthe heat exchanger is heated by combustion heat of a burner. As the heatexchanger becomes colder at the water entrance side, exhaust gas whichis performing heat exchange with cold water becomes low temperature,resulting that drain is generated.

On the other hand, since the heat exchanger becomes hot at the waterexit side, exhaust gas passing through the heat exchanger also becomeshot, thereby making it difficult to generate drain. Thus, generateddrain in a low temperature portion of the heat exchanger can beevaporated efficiently by hot exhaust gas passing through a hot portionthereof.

In other words, in the heat exchanger, heat is recovered from exhaustgas as much as possible without limiting drain generation. Thereafter,hot exhaust gas at a high temperature portion, which is generated bytemperature nonuniformity of the exhaust gas, evaporates drain generatedat a low temperature portion.

Consequently, high heat efficiency can be obtained without providing aplurality of heat exchangers, such as a main heat exchanger and asecondary heat exchanger in the exhaust gas route. Moreover, as draingenerated in the heat exchanger can be evaporated effectively, aneutralization apparatus can be omitted or simplified.

Therefore, it is possible to provide a hot water apparatus havingexcellent heat efficiency with low cost.

In the hot water apparatus according to the second aspect having theabove-mentioned configuration, a guide means guides drain generated atthe low temperature portion of the heat exchanger to a portion where hotexhaust gas flows. Therefore, drain is surely heated by hot exhaust gas.

Further, in the hot water apparatus according to the third aspect havingthe above-mentioned configuration, after drain generated at a lowtemperature portion of the heat exchanger is received by a drainreceiving and evaporating unit, it is guided to the side facing a hightemperature portion of the heat exchanger. While the drain is guided,the exhaust gas prompts the evaporation of the drain, and therefore, itis possible to evaporate drain more efficiently.

In the hot water apparatus according to the fourth aspect having theabove-mentioned configuration, after drain generated at a lowtemperature portion of the heat exchanger is received by a drainreceiving and evaporating unit, it is guided to the side facing a hightemperature portion of the heat exchanger by its own weight. Therefore,drain can be guided to a portion where hot exhaust gas flows without anydifficulties. Moreover, while the drain is guided, the exhaust gasprompts the evaporation of the drain, so that it is possible toevaporate drain more efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a water heater as one embodiment.

FIG. 2 is a cross-sectional view of a drain evaporator as oneembodiment.

FIG. 3 is a plain view of a drain evaporator as one embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

To clarify the above-described configuration and operation of thepresent invention, the preferred embodiment of the present inventionwill be explained below.

As shown in FIG. 1, a water heater 1 as one embodiment of the presentinvention includes a main body 2 having a combustion chamber 3 abovewhich a blower 5 connected with a DC motor 4 is provided. The main body2 has an inlet 6 for supplying air for combustion and an outlet 7 fordischarging exhaust gas to the upside of the inlet 6.

In the combustion chamber 3, provided are, from the upstream side, aburner 9 disposed on an installation plate 8 with a flame port reversedfor burning mixed gas made of fuel gas and primary air from the blower,a heat exchanger 10 of the fin tube type for recovering sensible heat ofexhaust gas from the burner 9 and latent heat of drain generatedtherein, a drain evaporator 11 for receiving and evaporating drain, andan exhaust gas hood 12 for discharging exhaust gas which heated the heatexchanger 10 and a drain evaporator 11. This exhaust gas hood 12 is abowl-shaped hood with a large opening facing the upper side. At thelateral side of the exhaust gas hood 12 an exhaust duct 13 is connected,whose opening at the upper end is directed to the outlet 7.

Water tubes provided in the main body 2 are, from the upstream side, acold water supply pipe 14 for supplying cold water, a winding tube 15which surrounds the combustion chamber 3 from the outside, a heattransfer tube 16 provided with the heat exchanger 10, and a hot wateroutlet 17 for discharging hot water. Among these water tubes, the heattransfer tube 16 is made of stainless steel with excellentcorrosion-proof, and the other tubes are made of copper.

The heat transfer tube 16 has many fins 18 which are made of stainlesssteel and disposed with even gaps for absorbing combustion heat. Becauseof this, the heat exchanger 10 is colder at the water entrance side, andwarmer at the water exit side. The fin gaps are designed so that at thewater exit side the temperature of passing exhaust gas is above the dewpoint (approximately 50-60 C.) in order to prevent drain generation, andat the water entrance side the temperature of passing exhaust gas is notlimited and thus heat exchange is performed until drain is generated.

As shown in FIGS. 1, 2 and 3, the drain evaporator 11 has a drainreceiving portion 20 and a drain cover 22. In the drain receivingportion 20, three elongate drain receivers 19, 19 and 19 are alignedtransversely, each of which is formed into U-shape in cross section andhas lateral ends connected integrally with each other. The drain cover22 is reverse U-shaped in cross section for covering the upper part ofthe exhaust gap 21 between the drain receivers 19, 19 and 19 to preventthe drain from dropping on the exhaust gas hood 12 etc. FIG. 2 is across sectional view taken along the chain line A-A shown in FIG. 1. Thedrain receiver 19 is bent to have the inclination of small degree, sothat a drain receiver guiding portion 28 and a drain evaporation portion29 are formed. On installation of the drain receivers 19, 19 and 19,when the drain evaporation portion 29 is disposed horizontally, thedrain receiver guiding portion 28 extends upward with an angle from thedrain evaporation portion 29.

The drain evaporator 11 is provided below the heat exchanger 10 andlarge enough to cover all the under area thereof. In the drainevaporator 11, the drain evaporation portion 29 is set horizontallyunder the water exit side of the heat exchanger 10. With thisconfiguration, the drain receiver guiding portion 28 is inclined, inwhich one end facing a low temperature portion of the heat exchanger 10,that is, its water entrance side is located at a higher position thanthe other end facing a high temperature portion of the heat exchanger10, that is, its water exit side.

The cold water supply pipe 14 has a water side control unit 23 having awater flow sensor or a water governor. A gas tube 24 for the burner 9has a main electromagnetic valve 25 and a proportional valve 26. Inaddition, the water flow sensor in the water side control unit 23, themain electromagnetic valve 25, the proportional valve 26 and the DCmotor 4 etc. are electrically connected to a burner controller 27 forcontrolling combustion of the water heater 1.

In the water heater 1 configured in this manner, when a water tap (notshown) is opened, water flows into the cold water supply pipe 14 (adotted arrow in the drawings), and a burner controller 27 detects asignal from the water flow sensor in the water side control unit 23 andperforms control operation. Then, the blower 5 starts to rotate drivenby the DC motor 4. When a predetermined purge is completed, the mainelectromagnetic valve 25 and the proportional valve 26 of the burner 9are opened and fuel gas (an arrow in the drawings) is supplied to theburner 9, and then the burner 9 is ignited by an igniter (not shown).

When the ignition is completed, proportional control is started. Thatis, if there is a difference between a set temperature and a temperaturedetected by a warm water temperature thermistor (not shown), the burnercontroller 27 detects the difference and sends a signal to theproportional valve 26, whereby an amount of fuel gas is continuouslychanged to maintain the temperature of hot water from the exit of theheat exchanger 10 at a predetermined level. Moreover, according tochanges of an amount of the fuel gas by means of the proportional valve26, the burner controller 27 sends a signal to the DC motor 4 of theblower 5 and rotating speed of the blower 5 is changed accordingly. As aresult, it is possible to obtain a predetermined relationship between anamount of fuel gas and air supply.

In this combustion control, along with the operation of the blower 5,air is suctioned into the main body 2 through the inlet 6 providedtherewith, and the air is guided to the burner 9 as combustion air.Around the flame port of the burner 9, mixed air is burned to generate aflame, and combustion is completed when the flame reaches to theupstream of the heat exchanger 10 (that is, complete combustion).

Hot exhaust gas from the burner 9 passes through gaps between the fins18 of the heat exchanger 10 by means of the blower 5 for heating waterwhich flows in the heat transfer tube 16. Thereafter, the exhaust gasheats the drain evaporator 11 and is discharged to the outside of theapparatus through the outlet 7. In the drain evaporator 11, the exhaustgas passes through a space between the drain cover 22 and the exhaustgap 21.

As the heat exchanger 10 becomes colder at its water entrance side, theexhaust heat becomes low temperature by heat exchange with flowingwater, whereby drain is generated. On the other hand, at its water exitside the heat exchanger is hot, so that the exhaust heat is still hoteven if passing through the heat exchanger 10, which prevents draingeneration.

The generated drain is received at the drain evaporator 11 providedright under the heat exchanger 10. Some of the drain falls down on thedrain cover 22 and is lead to the drain receiver 19. The drainevaporator 11 is disposed inclining so that its side facing the hightemperature portion of the heat exchanger is at a lower position. As aresult, the drain generated in the low temperature portion of the heatexchanger 10 drops on the drain receiver guiding portion 28, and movesby its own weight to the side facing the high temperature portion of theheat exchanger 10 where hot exhaust gas flows. Thereafter, the draincollected on the drain evaporation portion 29 is heated, whereby thedrain is evaporated. In this evaporation, the same amount of heat asthat of recovered latent heat is discharged to the exhaust gas, however,sensible heat can be recovered as much as possible without limitingdrain generation in the heat exchanger 10. Thereafter, hot exhaust gasat a high temperature portion, which is generated by temperaturenonuniformity of the exhaust gas, evaporates drain generated at a lowtemperature portion. It should be noted that the drain cover 22 alsoserves as a guide for temporarily guiding the exhaust gas to the drainin the drain receiver 19.

Consequently, high heat efficiency can be obtained without providing aplurality of heat exchangers, such as a main heat exchanger and asecondary heat exchanger in the exhaust gas route. Moreover, since draingenerated in the heat exchanger 10 can be evaporated effectively, aneutralization apparatus can be omitted or simplified.

Therefore, it is possible to provide a hot water heater 1 havingexcellent heat efficiency with low cost.

Moreover, after drain generated at a low temperature portion of the heatexchanger 10 is received by a drain evaporator 11, it is lead by its ownweight from the drain receiver guiding portion 28 to the drainevaporation portion 29, that is, the side facing a high temperatureportion of the heat exchanger 10. Therefore, drain can be guided to aportion where hot exhaust gas flows without any difficulties, so thatthe drain is heated by exhaust gas without fail.

Moreover, while the drain is guided in the drain receiver guidingportion 28, the exhaust gas prompts the evaporation of the drain, sothat it is possible to evaporate drain more efficiently. Moreover, theexhaust gas passes through a space between the drain cover 22 and theexhaust gap 21, so that the drain in the drain receiver 19 is heateddirectly by the exhaust gas. Therefore, the drain can be evaporated moreefficiently.

The above description of the embodiment of the present invention has inno way been provided for the purpose of limiting the present invention,and it is of course possible to diversely embody the present inventionwithin the scope not departing from the essential points of the presentinvention.

As an altered embodiment, it is possible to provide a simplifiedneutralization apparatus for neutralizing some of generated drain to bedischarged outside of an apparatus, unlike the present invention inwhich all generated drain is evaporated without discharging the sameoutside of an apparatus. In this case, all sensible heat as well as somelatent heat can be recovered when only the simplified neutralizationapparatus is provided, thereby heat efficiency can be further improved.

This invention is applicable to a hot water apparatus which heatsflowing water by combustion heat of a burner and discharges hot water.

1. A hot water apparatus comprising: a burner for burning fuel gas in acombustion chamber, and a heat exchanger for heating flowing water in aheat transfer tube by combustion heat of the burner, wherein draingenerated at a low temperature portion of the heat exchanger isevaporated by hot exhaust gas passing through a high temperature portionthereof.
 2. A hot water apparatus according to claim 1, furthercomprising a guide means for guiding the generated drain into a flowingroute of hot exhaust gas passing through the high temperature portion ofthe heat exchanger.
 3. A hot water apparatus according to claim 2,wherein the guide means has a drain receiving and evaporating unitprovided at the downstream of the exhaust gas route of the heatexchanger for receiving the drain, and said drain receiving andevaporating unit guides drain from the side facing the low temperatureportion of the heat exchanger to the side facing the high temperatureportion thereof.
 4. A hot water apparatus according to claim 2, whereinthe guide means has a drain receiving and evaporating unit provided atthe downstream of the exhaust gas route of the heat exchanger forreceiving the drain, and said drain receiving and evaporating unit isdisposed inclining so that its side facing the high temperature portionof the heat exchanger is at the lowest position.